U.S. patent number 10,537,676 [Application Number 15/766,859] was granted by the patent office on 2020-01-21 for sensing system for medication delivery device.
This patent grant is currently assigned to Eli Lilly and Company. The grantee listed for this patent is Eli Lilly and Company. Invention is credited to Phillip W. Barth, Mateusz B. Bryning, Leslie A. Field.
United States Patent |
10,537,676 |
Barth , et al. |
January 21, 2020 |
**Please see images for:
( Certificate of Correction ) ** |
Sensing system for medication delivery device
Abstract
A fluid sensing system (30) including a fluid channel (32) with
an inlet (34) and an outlet (36). A thermal device (38) is operably
coupled thereto at a first position whereby thermal energy is
transferable with fluid in the channel. A section of the fluid
channel downstream of the first position has a predefined cross
section and flow path. A thermal imaging device (46) is positioned
to capture a thermal image of at least a portion of the downstream
section. A processor (48) coupled with the thermal imaging device
is configured to determine at least one output value representative
of a property of the fluid medication or fluid flow using the
thermal image. The output value may be the flow volume. In some
embodiments, the fluid channel also defines a section upstream of
the first position with the thermal imaging device capturing an
image that includes at least portions of both the upstream and
downstream sections.
Inventors: |
Barth; Phillip W. (Portola
Valley, CA), Bryning; Mateusz B. (San Jose, CA), Field;
Leslie A. (Portola Valley, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Eli Lilly and Company |
Indianapolis |
IN |
US |
|
|
Assignee: |
Eli Lilly and Company
(Indianapolis, IN)
|
Family
ID: |
57233953 |
Appl.
No.: |
15/766,859 |
Filed: |
October 27, 2016 |
PCT
Filed: |
October 27, 2016 |
PCT No.: |
PCT/US2016/059099 |
371(c)(1),(2),(4) Date: |
April 09, 2018 |
PCT
Pub. No.: |
WO2017/079027 |
PCT
Pub. Date: |
May 11, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20180296756 A1 |
Oct 18, 2018 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
62250012 |
Nov 3, 2015 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61M
5/16836 (20130101); A61M 5/14 (20130101); A61M
5/16831 (20130101); A61M 5/172 (20130101); A61M
5/16886 (20130101); A61M 5/1723 (20130101) |
Current International
Class: |
A61M
5/168 (20060101); A61M 5/172 (20060101) |
Field of
Search: |
;250/338.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2012166168 |
|
Dec 2012 |
|
WO |
|
2014187432 |
|
Nov 2014 |
|
WO |
|
Primary Examiner: Porta; David P
Assistant Examiner: Gutierrez; Gisselle M
Attorney, Agent or Firm: Anderson; Jonathan
Claims
What is claimed is:
1. A fluid sensing system for a medication delivery device, the
medication delivery device including a reservoir adapted to contain
a supply of a fluid medication, and a discharge structure through
which the fluid medication is discharged from the medication
delivery device, the discharge structure being adapted to introduce
the fluid medication into a patient; the fluid sensing system being
disposed on the medication delivery device and comprising: a fluid
channel communicating the fluid medication from an inlet to an
outlet, the inlet being in fluid communication with the reservoir
with the reservoir being disposed upstream of the inlet, and the
outlet being in fluid communication with the discharge structure
with the discharge structure being disposed downstream of the
outlet; a thermal device operably coupled with the fluid channel at
a first position between the inlet and the outlet whereby thermal
energy is transferable between the thermal device and the fluid
medication flowing in the fluid channel at the first position and
wherein a downstream section of the fluid channel downstream of the
first position has a predefined cross section and a predefined flow
path; a thermal imaging device positioned to capture a thermal
image of at least a portion of the downstream section of the fluid
channel; and a processor coupled with the thermal imaging device
and configured to determine, based on at least one thermal image,
at least one output value that is representative of at least one
property of the fluid medication and/or the fluid flow in the fluid
channel, wherein the at least one output value includes at least
one of a flow volume of the fluid medication, a flow rate of the
fluid medication, an identity of the fluid medication, and a
concentration of a substance in the fluid medication.
2. The fluid sensing system of claim 1 wherein the fluid medication
is a liquid, and the processor is configured to determine the at
least one output value further based on a dimension of the
downstream section of the fluid channel.
3. The fluid sensing system of claim 1 wherein an upstream section
of the fluid channel upstream of the first position has a
predefined cross section and a predefined flow path and wherein the
thermal imaging device is positioned to capture a thermal image
including at least a portion of the upstream section in addition to
the portion of the downstream section.
4. The fluid sensing system of claim 3 wherein the downstream
section and the upstream section of the fluid channel define a
serpentine flow path.
5. The fluid sensing system of claim 1 wherein the fluid channel is
disposed on a substantially planar first layer of material.
6. The fluid sensing system of claim 5 further comprising second
and third layers of material defining the fluid channel, the first,
second and third layers each having a substantially consistent
thickness; the second layer being disposed on the first layer and
having a void defining the fluid channel; the third layer being
disposed on the second layer opposite the first layer whereby the
first layer and the third layer enclose the void defined by the
second layer.
7. The fluid sensing system of claim 6 wherein one of the first and
third layers is a glass substrate.
8. The fluid sensing system of claim 6 wherein the second layer has
a thickness within a range of 100 .mu.m to 500 .mu.m.
9. The fluid sensing system of claim 8 wherein the fluid channel
has a height substantially equivalent to the thickness of the
second layer and a width of approximately 2 mm.
10. The fluid sensing system of claim 6 wherein one of the first
and third layers is a thin film layer.
11. The fluid sensing system of claim 10 wherein the thin film
layer is a polylactic acid film.
12. The fluid sensing system of claim 6 wherein the first layer is
a layer substantially transparent to infrared light and the thermal
imaging device is positioned to capture an image facing the first
layer.
13. The fluid sensing system of claim 12 wherein the first layer is
formed out of a material selected from the group consisting of
silicon, polydimethylsiloxane (PDMS), germanium, zinc selenide,
silicon nitride, a thin film cyclo olefin polymer and a thin film
cyclo olefin copolymer.
14. The fluid sensing system of claim 6 wherein the first layer is
a thermally conductive layer substantially opaque to infrared light
and the thermal imaging device is positioned to capture an image
facing the opaque layer.
15. The fluid sensing system of claim 14 wherein the first layer is
formed out of a material selected from the group consisting of
metals, polymers, ceramics, glass, and polymer-ceramic
composites.
16. The fluid sensing system of claim 1 wherein the thermal device
is thermally coupled with an exterior surface of the fluid channel
whereby thermal energy is transferred between the thermal device
and the fluid medication through a wall of the fluid channel.
17. The fluid sensing system of claim 16 wherein the thermal device
and thermal imaging device are positioned on opposite sides of the
fluid channel.
18. The fluid sensing system of claim 1 wherein the thermal device
communicates thermal energy to the fluid medication in the fluid
channel to thereby increase the temperature of the fluid
medication.
19. The fluid sensing system of claim 18 wherein the thermal device
is an electrical resistor.
20. The fluid sensing system of claim 1 wherein the at least one
output value includes a flow volume of the fluid medication.
21. The fluid sensing system of claim 1 wherein the at least one
output value further includes at least one of a temperature of the
fluid medication, a heat capacity of the fluid medication, a
pressure of the fluid medication, a viscosity of the fluid
medication and a density of the fluid medication.
22. The fluid sensing system of claim 1 wherein the thermal imaging
device is spaced from and fixed relative to the fluid channel.
23. The fluid sensing system of claim 22 wherein the thermal
imaging device captures a two-dimensional image defining an aspect
ratio and wherein the fluid channel is disposed in a plane and
defines a serpentine flow path between the inlet and the outlet;
the serpentine flow path defining an overall length and overall
width in the plane wherein the ratio of the overall length and
overall width are substantially equivalent to the aspect ratio and
the thermal imaging device is positioned to capture an image
containing substantially all of the serpentine flow path between
the inlet and the outlet.
24. A fluid sensing system for a medication delivery device, the
medication delivery device including a reservoir adapted to contain
a supply of a fluid medication, and a discharge structure through
which the fluid medication is discharged from the medication
delivery device, the discharge structure being adapted to introduce
the fluid medication into a patient the fluid sensing system being
disposed on the medication delivery device and comprising: a fluid
channel communicating the fluid medication from an inlet to an
outlet, the inlet being in fluid communication with the reservoir
with the reservoir being disposed upstream of the inlet, and the
outlet being in fluid communication with the discharge structure
with the discharge structure being disposed downstream of the
outlet; a thermal device operably coupled with the fluid channel at
a first position between the inlet and the outlet whereby thermal
energy is transferable between the thermal device and the fluid
medication flowing in the fluid channel at the first position and
wherein a downstream section of the fluid channel downstream of the
first position has a predefined cross section and a predefined flow
path; a thermal imaging device positioned to capture a thermal
image of at least a portion of the downstream section of the fluid
channel; and a processor coupled with the thermal imaging device
and configured to determine, based on at least one thermal image,
at least one output value that is representative of a property of
the fluid medication and/or the fluid flow in the fluid channel,
wherein the fluid channel forms a helical coil and the thermal
imaging device is positioned to capture discrete discontinuous
portions of the downstream section of the fluid channel.
25. The fluid sensing system of claim 24 wherein the reservoir has
a columnar shape and the helical coil is wrapped about at least a
portion of the reservoir.
26. The fluid sensing system of claim 1 further comprising a fluid
pressure sensor, the fluid pressure sensor being operably coupled
with the fluid medication between the reservoir and the discharge
structure, the fluid pressure sensor being adapted to measure a
fluid pressure of the fluid medication.
27. The fluid sensing system of claim 26 wherein the second sensor
is a fluid pressure sensor.
28. The fluid sensing system of claim 1 wherein the discharge
structure is disengageable from the medication delivery device and
is thereby disposable after a single use.
29. The fluid sensing system of claim 28 wherein the fluid channel
is supported on the reservoir and the thermal imaging device and
processor are non-destructively separable from the reservoir and
the fluid channel whereby the reservoir and the fluid channel are
disposable after the contents of the reservoir have been
depleted.
30. The fluid sensing system of claim 1 wherein the discharge
structure is a hollow needle adapted to be inserted into a living
organism whereby the fluid medication can be injected into the
living organism.
31. The fluid sensing system of claim 1 wherein the reservoir
includes a feature having a thermally unique signature and whereby
the identity or authenticity of the reservoir and its contents are
detectable with the thermal imaging device.
32. A fluid sensing system for a medication delivery device, the
medication delivery device including a reservoir adapted to contain
a supply of a fluid medication, and a discharge structure through
which the fluid medication is discharged from the medication
delivery device, the discharge structure being adapted to introduce
the fluid medication into a patient the fluid sensing system being
disposed on the medication delivery device and comprising: a fluid
channel communicating the fluid medication from an inlet to an
outlet, the inlet being in fluid communication with the reservoir
with the reservoir being disposed upstream of the inlet, and the
outlet being in fluid communication with the discharge structure
with the discharge structure being disposed downstream of the
outlet; a thermal device operably coupled with the fluid channel at
a first position between the inlet and the outlet whereby thermal
energy is transferable between the thermal device and the fluid
medication flowing in the fluid channel at the first position and
wherein a downstream section of the fluid channel downstream of the
first position has a predefined cross section and a predefined flow
path; a thermal imaging device positioned to capture a thermal
image of at least a portion of the downstream section of the fluid
channel; and a processor coupled with the thermal imaging device
and configured to determine, based on at least one thermal image,
at least one output value that is representative of a property of
the fluid medication and/or the fluid flow in the fluid channel,
wherein a substrate structure defines the fluid channel and wherein
the substrate structure further defines at least one insulative
void.
33. The fluid sensing system of claim 32 wherein the insulative
void defines a slot extending entirely through the substrate
structure.
34. The fluid sensing system of claim 32 wherein the fluid channel
defines a serpentine path having a plurality of parallel path
segments and wherein the at least one insulative void comprises a
plurality of insulative voids with at least one of the plurality of
insulative voids being disposed between each pair of adjacent path
segments.
Description
BACKGROUND OF THE INVENTION
The present invention pertains to fluid delivery devices, and, in
particular, to a sensing system for determining volumetric flow or
other characteristics of the fluid being delivered.
A variety of known types of devices are used to deliver fluid
medication to a patient. Such delivery devices can be simple in
design, such as a standard syringe that is manually operated to
deliver medication through its attached needle, or can be more
complicated in design, such as infusion pumps that deliver
medication through a cannula.
For many delivery devices, the amount of fluid to be delivered
during an intended use is less than the complete medication
contents of that device. Especially for such delivery devices,
being able to determine or check the amount of fluid actually
delivered in a given use may be of high importance.
Many existing devices use a container or cartridge from which
medication is forced by advancement of a plunger within the
container barrel. Determining how far the plunger has moved, or how
far an element driving the plunger has moved, may serve as a proxy
for determining the volume of medication that has been delivered
from the device. However, such a means of determining the volume
may not always prove suitable, such as if the implementation is
overly complex, or the plunger is subject to large deformation, or
the movement of the driving element does not result in an output
that is readily useable by, for example, an electronic dosing
system.
Thus, it would be desirable to provide a sensing system, or a
delivery device that employs such a sensing system, that can
overcome one or more of these and other shortcomings of the prior
art.
SUMMARY OF THE INVENTION
The present invention provides a fluid sensing system that can be
used to determine a volumetric flow or other fluid or fluid flow
property and which is suitable for use with a dispensing device
such as a dispensing device used to inject a liquid medication into
a living organism.
The invention comprises, in one form thereof, a fluid sensing
system for a medication delivery device. The medication delivery
device includes a reservoir adapted to contain a supply of a fluid
medication and a discharge structure through which the fluid
medication is discharged from the medication delivery device, the
discharge structure being adapted to introduce the fluid medication
into a patient. The fluid sensing system is disposed on the
medication delivery device and includes a fluid channel
communicating the fluid medication from an inlet to an outlet. The
inlet is in fluid communication with the reservoir with the
reservoir being disposed upstream of the inlet. The outlet is in
fluid communication with the discharge structure with the discharge
structure being disposed downstream of the outlet. A thermal device
is operably coupled with the fluid channel at a first position
between the inlet and the outlet whereby thermal energy is
transferable between the thermal device and the fluid medication
flowing in the fluid channel at the first position. A downstream
section of the fluid channel downstream of the first position has a
predefined cross section and a predefined flow path. A thermal
imaging device is positioned to capture a thermal image of at least
a portion of the downstream section of the fluid channel and a
processor is coupled with the thermal imaging device and configured
to determine, based on at least one thermal image, at least one
output value that is representative of a property of the fluid
medication and/or the fluid flow in the fluid channel.
In some embodiments, the fluid medication is a liquid which, in
some embodiments, may be adapted for injection into a living
organism.
The fluid sensing system may also include an upstream section of
the fluid channel upstream of the first position which has a
predefined cross section and a predefined flow path wherein the
thermal imaging device is positioned to capture a thermal image
including at least a portion of the upstream section as well as a
portion of the downstream section. In such a system including an
upstream section, the downstream section and the upstream section
of the fluid channel may define a serpentine flow path. Alternative
embodiments may alternatively define a spiral or helix shaped flow
path.
In still other embodiments, the thermal imaging device is spaced
from and fixed relative to the fluid channel. In such an
embodiment, the thermal imaging device may be adapted to capture a
two-dimensional image defining an aspect ratio wherein the fluid
channel is disposed in a plane and defines a serpentine flow path
between the inlet and the outlet; the serpentine flow path defining
an overall length and overall width in the plane wherein the ratio
of the overall length and overall width are substantially
equivalent to the aspect ratio and the thermal imaging device is
positioned to capture an image containing substantially all of the
serpentine flow path between the inlet and the outlet.
In still other embodiments, the fluid sensing system has a fluid
channel that is disposed on a substantially planar first layer of
material. In such an embodiment, the system may further include
second and third layers of material defining the fluid channel,
wherein the first, second and third layers each have a
substantially consistent thickness with the second layer being
disposed on the first layer and having a void defining the fluid
channel and the third layer being disposed on the second layer
opposite the first layer whereby the first layer and the third
layer enclose the void defined by the second layer. In such
embodiments having first, second and third layers of material, one
of the first and third layers may take the form of a glass
substrate. It is also possible to employ a plastic substrate.
In yet other alternative embodiments of the fluid sensing system
wherein first, second and third layers form the fluid channel, the
second layer may advantageously have a thickness within a range of
100 .mu.m to 500 .mu.m. In such an embodiment, the fluid channel
may have a height substantially equivalent to the thickness of the
second layer and a width of approximately 2 mm.
Various other embodiments are also possible, for example, one of
the first and third layers may take the form of a thin film layer.
Such a thin film layer may be advantageously formed out of a
polylactic acid (PLA) film, e.g., a 25 .mu.m thick film.
In still other embodiments of the fluid sensing system wherein
first, second and third layers form the fluid channel, the first
layer may be a layer substantially transparent to infrared light
with the thermal imaging device being positioned to capture an
image facing the first layer. In such an embodiment, the
substantially transparent layer may be formed out of silicon,
polydimethylsiloxane (PDMS), germanium, zinc selenide, silicon
nitride (conventional or low stress), thin film cyclo olefin
polymer, thin film cyclo olefin copolymer or other suitable
material. Cyclo olefin polymers and cyclo olefin copolymers, such
as those available under the tradenames Zeonor and Zeonex, may also
be used to form a substantially transparent layer. In this regard,
it is noted that cyclo olefin polymers and copolymers are not
entirely transparent to infrared light in the typical range of
thermal imaging devices, a sufficiently thin film of such material
will be suitably transparent. Similarly, many materials not
typically considered infrared transparent, will be infrared
transparent when formed in a sufficiently thin film.
In yet other embodiments of the fluid sensing system wherein first,
second and third layers form the fluid channel, the first layer may
be a thermally conductive layer substantially opaque to infrared
light with the thermal imaging device being positioned to capture
an image facing the opaque layer. In such an embodiment, the opaque
layer may be formed out of metals, polymers, ceramics, glass,
polymer-ceramic composites or other suitable material.
In other embodiments of the fluid sensing system, the thermal
device may be thermally coupled with an exterior surface of the
fluid channel whereby thermal energy is transferred between the
thermal device and the fluid medication through a wall of the fluid
channel. In such an embodiment, the thermal device and thermal
imaging device may be advantageously positioned on opposite sides
of the fluid channel.
In some embodiments of the fluid sensing system the thermal device
communicates thermal energy to the fluid medication in the fluid
channel to thereby increase the temperature of the fluid
medication. In such an embodiment, the thermal device may
advantageously take the form of an electrical resistor. Alternative
embodiments may employ other forms of thermal devices such as a
light emitting diode (LED) or laser.
In still other embodiments of the fluid sensing system, the at
least one output value advantageously includes a flow volume of the
fluid medication. In yet other embodiments of the fluid sensing
system, the at least one output value includes a volumetric flow
rate of the fluid medication, an identity of the fluid medication,
a concentration of a substance in the fluid medication, a
temperature of the fluid medication, a heat capacity of the fluid
medication, a pressure of the fluid medication, a viscosity of the
fluid medication and/or a density of the fluid medication. An
additional sensor, such as a fluid pressure, may be added to the
system to thereby measure a second fluid property and thereby aid
in the determination of the various fluid parameters.
In some embodiments of the fluid sensing system, the fluid channel
forms a helical coil and the thermal imaging device is positioned
to capture discrete discontinuous portions of the downstream
section of the fluid channel. In such embodiments having a helical
fluid channel, the reservoir may have a columnar shape with the
helical coil formed by the fluid channel being wrapped about at
least a portion of the reservoir.
In still other embodiments of the fluid sensing system, the system
may additionally include a second sensing device wherein the second
sensing device is operably coupled with the fluid medication
between the reservoir and the discharge structure such that the
second sensing device is adapted to measure a property of the fluid
medication. The second sensor may advantageously take the form of a
fluid pressure sensor such as a micro electro-mechanical system
(MEMS) fluid pressure sensor.
In yet other embodiments of the fluid sensing system, the discharge
structure may be disengageable from the medication delivery device
whereby the discharge structure is disposable after a single use.
For example, the discharge structure may be an injection needle
which is detached and discarded after use. In such an embodiment,
the fluid channel may be supported on the reservoir with the
thermal imaging device and processor being non-destructively
separable from the reservoir and the fluid channel. This allows the
reservoir and fluid channel to be disposed of after the contents of
the reservoir have been depleted while re-using the thermal imaging
device and processor.
In some embodiments, the discharge structure advantageously takes
the form of a hollow needle adapted to be inserted into a living
organism whereby the fluid medication can be injected into the
living organism.
In some embodiments, the reservoir includes a feature having a
thermally unique signature and whereby the identity or authenticity
of the reservoir and its contents can be checked with the thermal
imaging device.
In some embodiments, the fluid sensing system includes a substrate
structure defining the fluid channel wherein the substrate
structure also defines at least one insulative void. In such an
embodiment, the insulative void may define a slot that extends
entirely through the substrate structure. For an embodiment with an
insulative void, the embodiment may include a plurality of such
insulative voids and the fluid channel may define a serpentine path
having a plurality of parallel path segments and wherein at least
one of the plurality of insulative voids is disposed between each
pair of adjacent path segments.
One advantage of the present invention is that a system for sensing
volumetric flow may be provided for a medication delivery
device.
Another advantage of the present invention is that a system for
sensing volumetric flow may be provided for a medication delivery
device in which no sensors need be placed in contact with the
medication. The use of non-contact components also facilitates the
potential re-use of such non-contact components.
Another advantage of the present invention is that a system for
sensing characteristics of a medication in a delivery device may be
provided in a compact and convenient fashion.
BRIEF DESCRIPTION OF THE DRAWINGS
The above mentioned and other features of this invention, and the
manner of attaining them, will become more apparent and the
invention itself will be better understood by reference to the
following description of an embodiment of the invention taken in
conjunction with the accompanying drawings, wherein:
FIG. 1 is a schematic representation of a delivery device employing
a fluid sensing system.
FIG. 2 is a top view of a fluid channel and heating device for use
in fluid sensing system.
FIG. 3 is a schematic side view of a fluid sensing system.
FIG. 4 is a schematic cross section through a portion of the fluid
sensing system fluid channel.
FIG. 5 is a schematic representation of an infrared image for use
in a fluid sensing system illustrating a low flow rate.
FIG. 6 is a schematic representation of an infrared image for use
in a fluid sensing system illustrating a medium flow rate.
FIG. 7 is a schematic representation of an infrared image for use
in a fluid sensing system illustrating a high flow rate.
FIG. 8 is a schematic representation of an alternative delivery
device employing a fluid sensing system.
FIG. 9 is a schematic representation of another alternative
delivery device employing a fluid sensing system.
FIG. 10 is a schematic representation of yet another alternative
delivery device employing a fluid sensing system.
FIG. 11 is a schematic representation of still another alternative
delivery device employing a fluid sensing system.
FIG. 12 is a schematic representation of another fluid sensing
system.
FIG. 13 is a schematic cross section of the fluid sensing system
taken along line 13-13 of FIG. 12.
Corresponding reference characters indicate corresponding parts
throughout the several views. Although the exemplification set out
herein illustrates a embodiments of the invention, in several
forms, the embodiments disclosed below are not intended to be
exhaustive or to be construed as limiting the scope of the
invention to the precise forms disclosed.
DETAILED DESCRIPTION OF THE INVENTION
A medication delivery device 20 is schematically depicted in FIG.
1. Medication delivery device 20 take various forms such as an
injection device, e.g., an injection pen, an infusion device, e.g.,
an infusion pump, or other device for providing a medication fluid
to a patient. Medication delivery device 20 includes a reservoir 22
containing a supply of the fluid 24 to be dispensed by device 20.
In the illustrated example, fluid 24 is a liquid medication
intended to be injected into a living organism. In some
embodiments, reservoir 22 may take the form of a disposable
cartridge containing one or more doses of a liquid medication such
as insulin.
As can also be seen in FIG. 1, device 20 includes a discharge
structure 26 through which the fluid medication 24 is expelled. In
the illustrated example, structure 26 is a hollow needle which can
be inserted into a living organism to thereby allow fluid
medication 24 to be injected into the organism. For example, the
living organism might be a human being who has diabetes and
requires periodic injections of insulin. A driving mechanism 28 is
coupled with the fluidic system and provides the means for causing
fluid to flow from reservoir 22 toward discharge structure 26.
Various driving mechanisms 28 may be used depending upon the
application for which device 20 is adapted. For example, driving
mechanism 28 might advantageously take the form of an electrically
powered infusion pump. Although it will often be desirable to
employ an automated driving mechanism 28, it would also be possible
to employ a spring driven or manually operated plunger for
discharging the contents of reservoir 22.
Device 20 also includes a fluid sensing system 30 which senses the
flow of fluid and, in the illustrated embodiment, does not require
contact with the fluid. Fluid sensing system 30 is disposed on
device 20, for example, it may be located entirely or partially
within the housing of device 20. Fluid sensing system 30 is
disposed between reservoir 22 and discharge structure 26 to thereby
measure and/or monitor a fluid flow parameter of the flow of fluid
medication 24 from reservoir 22 to discharge structure 26. For
example, sensing system 30 could be used to measure or monitor the
volumetric flow or flow volume of fluid medication 24. In other
words, it can be used to measure the total volume of fluid
medication 24 that flows past the point being monitored. When the
fluid flow is not diverted and there are no intermediate
reservoirs, a measurement of the flow volume will also correspond
to the volume of fluid medication 24 discharged through discharge
structure 26. This measurement can be particularly useful when
device 20 is used to dispense a fluid medication where the
dispensed quantity is of significant importance. Sensing system 30
can also be used to measure or monitor the volumetric flow rate of
fluid medication 24. This can be useful for control purposes, and,
when combined with the elapsed time of the flow, the measurement is
also useful to determine the volume of fluid discharged through
discharge structure 26. The measurement of flow volumes and
volumetric flow rates by sensing system 30 is discussed in greater
detail below.
Fluid sensing system 30 includes a fluid channel 32 that
communicates fluid medication 24 from an inlet 34 to an outlet 36.
As can be seen in FIG. 1, reservoir 22 is disposed upstream of
inlet 34 and discharge structure 26 is disposed downstream of
outlet 36. In some embodiments, inlet 34 and outlet 36 may be
distinct physical structures. In other embodiments, however, inlet
34 and outlet 36 are simply non-distinct points on a continuous
fluid channel demarking that portion of the fluid channel
associated with fluid sensing system 30.
A thermal device 38 is coupled with fluid channel 32 at a location
40 between inlet 34 and outlet 36. Downstream of location 40 is a
downstream section 42 of fluid channel 32 that extends from
location 40 to outlet 36. Upstream of location 40 is an upstream
section 44 that extends from inlet 34 to location 40.
A thermal device 38 is operably coupled with fluid channel 32 at
location 40 to provide for the transfer of thermal energy between
the thermal device 38 and fluid medication 24 flowing in the fluid
channel 32 at location 40. Thermal device 38 could be either a
heating or cooling device. For example, thermal device 38 could be
cooling device that absorbs thermal energy from fluid medication 24
to thereby cool the fluid. Such a cooling device might include a
heat pipe or a thermal heat sink which has been cooled to a
temperature below that of the fluid in reservoir 22.
Alternatively, thermal device 38 could be a heating device that
communicates thermal energy to the fluid medication 24 in the fluid
channel 32 at location 40 to thereby increase the temperature of
the fluid medication 24. For example, in the illustrated example,
thermal device 38 is an electrical resistor that experiences a
temperature increase and transfers thermal energy to fluid
medication 24 when electrical current is passed therethrough. In
the illustrated embodiment (FIG. 3), an electrical power supply 37,
for example, a battery, supplies electrical current to resistor 38
which is a 200 Ohm resistor. Processor 48 is advantageously coupled
with power supply 37 to regulate the supply of electrical current
to resistor 38.
Various other alternative devices may be used to provide a thermal
device 38. For example, a Peltier (thermoelectric) device (TEC), a
light source such as a laser or LED, or a passive mechanism such as
the body heat of the user could be employed to provide a thermal
device 38.
Thermal device 38 can be thermally coupled with fluid medication 24
by thermally coupling it with the exterior surface 39 of fluid
channel 32 whereby thermal energy is transferred between thermal
device 38 and fluid medication 24 through a wall 33 of fluid
channel 32. For example, electrical resistor 38 can be attached to
exterior surface 39 of fluid channel 32 to thereby communicate
thermal energy to fluid medication 24 through fluid channel wall
33. Alternatively, a thermal device 38 could be integrated into the
fluid channel structure and form a portion of the interior surface
of the fluid channel and thereby provide for the direct transfer of
thermal energy between thermal device 38 and fluid medication 24.
In yet other embodiments, the thermal device 38 may be spaced from
fluid channel 32 to provide for non-contact thermal transfer. For
example, thermal device 38 could be a laser or LED to provide for
non-contact heating.
Thermal device 38 is used to create a local variation in the
temperature of the fluid flowing in fluid channel 32. For example,
fluid medication 24 in reservoir 22 might be at the ambient
temperature and thermal device 38 will either raise or lower the
temperature of fluid medication 24 at location 40. The temperature
of fluid medication 24 would then move toward the ambient
temperature as it flows downstream from location 40. For some
applications, the system may be designed so that the fluid returns
to ambient temperature by the time it reaches outlet 36. In some
applications, however, fluid medication 24 in reservoir 22 may be
at a temperature that differs from the ambient temperature, e.g.,
fluid medication 24 might be maintained in a chilled condition
prior to injection. In such applications, it might also be
desirable to employ a heating element between fluid sensing system
30 and discharge structure 26 to bring the fluid to the desired
temperature before discharge.
For example, in some applications, it may be desirable to inject
fluid medication 24 at body temperature which is typically much
higher than the ambient temperature. In such an application, the
fluid medication 24 may have a temperature greater than the ambient
temperature when it reaches location 40 where it is either heated
or chilled. It will move then begin moving toward ambient
temperature. The initial temperature of the fluid and the amount of
heat either added or removed at location 40 can be selected such
that the fluid is at the desired temperature when it is discharged
regardless of whether the desired temperature at discharge is the
ambient temperature or some other temperature.
Depending upon the fluid flow parameters being measured with system
30 and the application of system 30, thermal device 38 may be used
to provide either constant heating or cooling or a pulsed heating
or cooling. The use of pulsed heating/cooling may be useful in
preventing the degradation of pharmaceutical compounds or other
sensitive fluids.
The magnitude of the local temperature variation generated by
thermal device 38 will vary depending upon the particular
application of system 30. For example, sensitivity and resolution
of the imaging device 46 will have an impact on the magnitude of
the temperature variation best suited for a particular application.
It is anticipated that a maximum magnitude of the local temperature
variation which would be sufficient is on the order of less than
10.degree. C. In some applications, the magnitude of the local
variation may be as small as 1.degree. C. or even a fraction of
1.degree. C. In other embodiments, the magnitude of the variation
could exceed 10.degree. C.
In some applications, a feedback loop may be beneficially employed
with thermal device 38. Such a feedback loop could monitor the
temperature of thermal device 38 and adjust the operating
parameters thereof, e.g., current flowing to a resistor, to ensure
stable operation. This type of feedback loop could be integrated
into sensing system 30 using processor 48 and thermal imaging
device 46 as the monitoring device. Alternatively, a separate
circuit that includes a thermocouple and an independent controller
could be used. Some applications might also benefit from the use of
high-precision temperature control methods such as the use of a
proportional-integral-derivative (PID) controller for temperature
control.
A thermal imaging device 46 is positioned to capture a thermal
image of at least a portion of the downstream section 42 of fluid
channel 32. A processor 48 is coupled with thermal imaging device
46 and is configured to determine at least one output value as a
function of the thermal image as discussed in greater detail below.
In other words, the thermal image is processed to assess a
characteristic of the fluid in channel 32. Advantageously, this
analysis of the thermal image will determine the flow volume and/or
volumetric flow rate of fluid medication 24 in channel 32.
The output value may optionally be communicated to a user with an
output device 50 such as a display, e.g., a liquid crystal display
(LCD) screen. Alternatively, the output value may be used by
processor 48 for another purpose, e.g., the system may determine
the heat capacity of the fluid to assess the concentration of
active medication in a fluid carrier, without communicating the
value to the user.
Thermal device 38 can be positioned either in or outside the field
of view of thermal imaging device 46. By placing the thermal device
outside the field of view, the imaging artifacts and interference
potentially caused by thermal device 38 can be reduced. Regardless
of whether or not the thermal imaging device 38 is within the field
of view of thermal imaging device 46, it will generally be
advantageous to include at least a portion of both the downstream
42 and upstream section 44 of the fluid channel 32. The inclusion
of at least a portion of the upstream section 44 can be useful for
purposes of providing a reference temperature for calibration.
It is noted that by extending one leg of the serpentine path shown
in FIG. 2 beyond the limits of the field of view, thermal device 38
could be placed outside the field of view while still including a
substantial portion of both upstream and downstream sections of
channel 32 in the field of view. Alternatively, thermal device 38
and thermal imaging device 46 can be positioned on opposite sides
of fluid channel 32 as schematically depicted in FIG. 1 to limit
the interference of thermal device 38 itself when capturing a
thermal image with device 46. In the illustrated embodiment, the
thermal imaging device 46 is spaced from and fixed relative to
fluid channel 32 such that the portion of fluid channel 32 captured
in the images remains constant. For example, both thermal imaging
device 46 and fluid channel 32 can be fixed relative to housing 29
or other common structure.
As best seen in FIGS. 2 and 5-7, in the illustrated embodiment,
fluid channel 32 defines a flow path having a serpentine shape.
This shape is advantageous because it allows a longer length of the
flow path to be captured in a single thermal image. In the
exemplary embodiment, thermal imaging device 46 captures a
two-dimensional thermographic image 47 representing the radiation
in the infrared range of the objects in the field of view. FIGS.
5-7 are schematic representations of such images 47.
Like a conventional camera, device 46 has an aspect ratio that
corresponds to the ratio of the height (H.sub.2) to width (W.sub.2)
of image 47 captured by device 46 (FIG. 5). A typical aspect ratio
might be 3:4. By configuring fluid conduit 32 to lie in a plane and
have a serpentine shape with an overall length (L.sub.1) and an
overall width (W.sub.1) (FIG. 2) such that the ratio of
L.sub.1/W.sub.1 is substantially equivalent to H.sub.2/W.sub.2 and
positioning thermal imaging device 46 to face perpendicular to the
plane of channel 32 at an appropriate distance from fluid channel
32, substantially all of the serpentine flow path between inlet 34
and outlet 36 can be captured in thermal image 47 without any
significant wasted image potential. While the use of a serpentine
shape provides advantages, alternative configurations, such as a
spiral or linear flow path, can alternatively be used.
The most suitable shape for the fluid channel will depend upon a
number of factors, most significantly the anticipated flow rate.
For example, the serpentine shape depicted in FIGS. 2 and 5-7 is
well-suited for determining flow volume and flow rate in medium to
high flow rates applications. A linear flow path is well suited for
determining flow volume and flow rate in a low flow rate
application. A three-dimensional helical coil configuration for the
flow path where discrete non-continuous sections of the flow path
are imaged may be useful when determining flow volume and flow rate
for relatively high flow rates. When fluid properties other than
flow volume and flow rate are being assessed, it may be beneficial
to include additional or alternative features in the flow channel.
For example, it may be advantageous to use a relatively wide
channel that includes obstacles or features such as pillars in the
flow channel or irregular or serrated side walls to thereby impact
the flow and facilitate obtaining additional data. A side chamber
in communication with the flow channel and which includes a second
sensing device such as a pressure sensor could also be employed.
Such additional features and sensing device may be particularly
helpful when determining fluid properties beyond the flow volume
and flow rate such as the viscosity, pressure or other
property.
Thermal imaging device 46 can take the form of an infrared (IR)
camera. Such IR cameras are commercially available and can be
adapted for use in system 30. For example, IR cameras are
commercially available that can be connected with a smart phone to
capture thermal images. Also commercially available are IR camera
chips that can be incorporated into applications without requiring
connection to a smart phone. For example, an IR camera chip sold
under the trademark Lepton.RTM. is commercially available from FLIR
Systems, Inc. and can be used in fluid sensing system 30. Some of
the factors that will influence the selection of the thermal
imaging device 46 will be whether the size of the device (smaller
will generally be more desirable), the power requirements of the
device (low electrical power requirements will generally be more
desirable), the thermal sensitivity and the resolution (number of
pixels) are adequate for the intended application. The
determination of some fluid properties will require a greater
thermal sensitivity and/or resolution than other fluid properties.
For example, if the sensing system is used to determine a
concentration or identity of the fluid, it will require a greater
thermal sensitivity and resolution than if it is merely used to
determine a flow volume or flow rate. A second sensor, such as a
fluid pressure sensor, might also be necessary for determining some
fluid properties beyond the flow volume and flow rate. The use of
one or more additional sensors may also allow for the selection of
a thermal imaging device having a lower resolution. Such sensors
could include any number of different known fluid sensors in
addition to a fluid pressure sensor that might be useful for a
particular application.
It is additionally noted, that most commercially available thermal
imaging devices have thermal sensitivities on an order of magnitude
of 0.01.degree. C. and will have the necessary thermal sensitivity
for use in the devices described herein. Commercially available
thermal imaging devices can be obtained in a range of different
resolutions with higher resolution devices being more expensive. As
a result, it will generally be desirable to use a thermal imaging
device with the lowest resolution that is adequate for the intended
application.
In the exemplary embodiment, thermal imaging device 46 is a FLIR
Lepton.RTM. having a spectral range in the longwave infrared
spectrum of approximately 8 .mu.m to approximately 14 .mu.m; a
thermal sensitivity of less than 50 mK (0.050.degree. C.) and an
output format that is user selectable and may be 14-bit, 8-bit (AGC
applied), or 24-bit RGB (AGC and colorization applied).
Returning to a discussion of fluid channel 32, it is noted that in
the illustrated example, middle layer 54 defines the plane in which
fluid channel 32 is disposed. Alternative arrangements to provide
for a substantially planar serpentine flow path, however, may also
be used to maximize the utilization of the imaging capabilities of
device 46. To maintain the shape of the flow path in a predefined
configuration, it will often be desirable to mount or form the
fluid channel on a rigid substrate.
In the exemplary embodiment, a multi-layered structure is used to
form fluid channel 32 and maintain its shape. The structure of the
exemplary embodiment is best understood with reference to FIGS. 3
and 4. In this embodiment, fluid channel 32 is defined by three
layers of material. More specifically, the illustrated example
includes a relatively thick outer layer 52, a center layer 54 and a
thin film outer layer 56. Outer layer 52 functions as a rigid
planar substrate for fluid channel 32. By having fluid channel 32
disposed on a substantially planar, rigid structure, it maintains
the predefined shape of the flow path to facilitate capturing
thermal images thereof.
A void 58 is formed in middle layer 54 to define the layout and
width of fluid channel 32. Outer layers 52, 56 are disposed on the
opposite sides of middle layer 54 whereby layers 52, 56 enclose the
void 58 formed in middle layer 54 and thereby define fluid channel
32. In the illustrated embodiment, layers 52, 54 and 56 are each
substantially planar and have differing thicknesses. Alternative
embodiments, however, may employ either greater or fewer layers and
wherein some or all of the layers have a substantially constant
thickness.
In the illustrated embodiment, layer 52 is a substantially planar
layer of material which takes the form of a glass substrate. The
use of a glass substrate provides a planar rigid structure that
maintains fluid channel 32 in a predefined shape. Alternative
embodiments, however, can utilize other structures to maintain the
configuration of fluid channel 32. For example, instead of relying
upon the rigidity of a single layer of material, the combined
structural strength of two or more of the layers forming channel 32
could provide the rigidity to maintain the shape of fluid channel
32. Still other methods could also be employed, for example, a
flexible fluid channel could be fixed to a rigid support member.
While it will generally be desirable to maintain fluid channel 32
in a plane to facilitate the processing of the thermographic
images, it is not essential for fluid channel 32 to be maintained
in a plane and, particularly if other considerations dictate an
alternative arrangement, a non-planar configuration of fluid
channel 32 could be employed. An example of such a non-planar
configuration is discussed below when describing the embodiment of
FIGS. 10 and 11.
In addition to a predefined flow path shape, fluid channel 32 also
has a predefined cross sectional shape (FIG. 4). The cross
sectional shape of channel 32 can vary or remain constant over the
length of the fluid channel 32. The desirability of maintaining a
constant cross sectional shape will depend in part on the fluid
flow parameters which will be determined based upon the
thermographic images captured by device 46. In the exemplary
embodiment, the cross sectional shape and area is maintained
substantially constant over the length of fluid channel 32 between
inlet 34 and outlet 36.
In the exemplary embodiment, it is the void space 58 in layer 54
that defines the layout of the flow path and width of channel 32
while the two outer layers 52, 56 define the height of the
substantially rectangular fluid channel 32. As discussed above, the
layout of the flow path defines a serpentine shape in the
illustrated embodiment. In the exemplary embodiment, middle layer
54 has a thickness 60 of approximately 100 .mu.m. Because void 58
extends the full thickness of layer 54 without extending beyond the
limits of layer 54, fluid channel 32 has a height 62 substantially
equivalent to the thickness 60 of middle layer 54. The width 64 of
channel 32 is approximately 2 mm in the illustrated embodiment. For
the exemplary embodiment, channel 32 maintains a substantially
constant cross sectional shape having the approximate dimensions of
100 .mu.m by 2 mm for the entire length of downstream section 42
and upstream section 44.
The optimal dimensions of the fluid channel will depend
significantly upon the anticipated flow rate of the fluid through
the channel. For example, when using a medical delivery device to
inject a liquid medicament into a patient, the flowrate will often
be between 0.5 milliliter/minute and 15 milliliter/minute. At this
flowrate, a channel having a width of 2 mm and a depth within the
range of 100 .mu.m to 500 .mu.m will often be suitable. For many
such applications involving the injection of a liquid medicament,
the length of such a fluid channel within the field of view of the
imaging device may advantageously be between 200 mm and 250 mm. For
example, a suitable channel might have a width of 2 mm, a depth of
500 .mu.m and a length of 222 mm.
It is further noted that when using a serpentine flow channel, the
distance separating the parallel sections of the flow channel is
subject to competing design objectives. Reducing the distance
between the parallel sections of fluid channel helps to minimize
the footprint of the sensing system and maximize the length of the
flow channel within the field of view of the imaging device.
However, if the distance becomes too small, thermal interference
between adjacent fluid sections can arise. Reducing the separation
distance between channel sections can also increase manufacturing
costs. When using a channel having a width of 2 mm and a depth of
500 .mu.m, a separation distance of 3 mm balances many of the
competing design objectives and allows the channel to be cost
effectively manufactured using laser machining.
Middle layer 54 may be formed out of a metal, silicon, or other
suitable material. A thin film layer may be used to form an outer
layer 56. For example, layer 56 may be formed using a polylactic
acid film. Alternatively, layer 56 and/or layer 52 could be formed
using a cyclic olefin compound or a cyclic olefin copolymer. As
discussed in greater detail below, one of the outer layers 52, 56
is adapted to facilitate the capture of a thermographic image that
is representative of the thermographic profile of fluid medication
24 flowing within channel 32.
Middle layer 54 forming fluid channel 32 advantageously acts as a
thermal insulator inhibiting the transfer of heat from one leg of
channel 32 to an adjacent leg of channel 32. Advantageously, middle
layer 54 has lower thermal conductivity than the outer layer 52 or
56 which faces thermal imaging device 46. The outer layer 52 or 56
opposite thermal imaging device 46 may also advantageously have a
thermal conductivity that is lower than the outer layer facing
thermal imaging device 46. By providing the middle layer 54 and the
outer layer opposite thermal imaging device 46 with greater thermal
insulative properties relative to the outer layer facing thermal
imaging device 46, the transfer of thermal energy between adjacent
legs of channel 32 is less likely to occur. This, in turn, provides
a better thermal profile for capture by thermal imaging device 46.
For some applications, it might also be advantageous for one of the
layers to form or be in thermal communication with a heat sink. For
example, such a layer might be positioned on the opposite side of
thermal imaging device 46 and facilitate the achieving of the
desired discharge temperature of the fluid.
Middle layer 54 can be provided with enhanced thermal insulative
properties by infusing an insulative material in layer 54 or
providing layer 54 with an insulative coating. Similarly, the outer
layer opposite thermal imaging device 46 could be infused or coated
with an insulative material. If an insulative coating is used, it
is advantageously applied to at least the channel walls 33 defined
by middle layer 54 and the outer layer disposed opposite thermal
imaging device 46. Various different materials, such as polymers,
adhesives with insulative properties, or other conventional coating
materials having suitable physical properties may be used.
Conventional coating technologies can be used to apply the coating
such as spray, spin, sputtering and plasma coating applications.
The various forms of vacuum coating technologies, such as chemical
vapor deposition (CVD), plasma enhanced chemical vapor deposition
(PECVD) and the like, may also be used. Conventional screen
printing techniques may be used to control the application of the
coating to the desired location. MEMS (microelectromechanical
systems), microfluidic, and IC (integrated chip) manufacturing
techniques may also be used to manufacture the fluid channel and
supporting substrate.
FIGS. 12 and 13 illustrate an alternative embodiment which utilizes
voids in the rigid substrate forming the fluid channel to enhance
the thermal isolation of discrete sections of the fluid channel.
When an enclosed fluidic channel 32 meanders back and forth to form
a serpentine path within a generally planar substrate in order to
maximize the fluid path length visible to a camera, the problem of
interactions between adjacent legs of the serpentine channel can
arise. If the camera is an infrared camera which senses the
temperature of the fluid, or which senses the temperature of the
exposed surface of the channel containing the fluid, there arises
the possibility that heat can bleed from one leg of the serpentine
channel to an adjacent leg of the channel, thereby raising the
temperature of that adjacent leg in an undesired manner. In order
to prevent this undesired occurrence, it is advantageous to include
a thermal isolation feature between adjacent channels. Using a
thermal isolation feature blocks the undesired lateral flow of heat
between adjacent channels, thereby ensuring that most heat flow
occurs longitudinally in the channel in the direction of fluid flow
where it can provide a signal related to the flow magnitude or
perpendicular to the exposed surface of the structure defining the
fluid channel into the ambient environment.
A thermal isolation feature for the above purpose may take the form
of a region between adjacent legs of the fluid path wherein the
thermal conductivity of the thermal isolation feature is very much
less than the thermal conductivity of either the flowing fluid, or
the channel walls enclosing the fluid, in two adjacent legs of the
channel. As discussed above, one method of providing such a thermal
isolation region is the use of insulative materials between
adjacent legs of the serpentine flow path. Such a region may also
advantageously take the form of a void filled with a gas or vacuum
wherein the void is located between the walls of the two adjacent
fluid channel legs. A vacuum has essentially zero thermal
conductivity, while gases including air and sulfur hexafluoride
have thermal conductivities which are much less than the thermal
conductivities of solid materials, such as plastics, polymers,
glasses, and the like.
The thermally isolative void 90 may take the form of a narrow slot
created through the substrate, and different slots can be situated
at different locations on the substrate structure.
Voids 90 may extend completely through the substrate structure in
which the fluidic channels are enclosed. Alternatively, voids 90
may be bounded on one or both planar surfaces of the substrate
structure by thin regions which provide mechanical integrity to the
substrate structure while constituting only a minor thermal
conduction path compared to the thermal conduction path which would
be present if voids 90 were not used.
If slots 90 extend entirely through the substrate structure, small
support sections 92 are used to maintain the structural integrity
of the overall substrate structure. Even when the slots do not
extend entirely through the substrate structure, providing such
support sections 92 may still be desirable to enhance the strength
of the substrate structure. While such support sections 92 do
provide a thermal bridge, such section provide only a minor thermal
conduction path compared to the thermal conduction path which would
be present if voids 90 were not used.
FIG. 12 depicts a substrate structure 94 defining a fluid channel
32 having a serpentine path with a plurality of substantially
parallel adjacent path segments 96, 98, 100, 102, 104, 106. As can
be seen in FIG. 12, insulative voids 90 are disposed proximate the
fluid channel 32 to inhibit transfer of thermal energy from the
fluid in channel 32 through the substrate structure 94. Support
sections 92 periodically interrupt voids 90 to provide structural
strength. The voids 90 have low thermal conductivity and provide
thermal isolation between adjacent path segments 96, 98, 100, 102,
104, 106. The support sections 92 provide the substrate structure
94 with structural integrity in the same way that support regions
in a stencil keep the stencil from falling apart.
FIG. 13 provides a schematic cross sectional view of two
alternative embodiments of insulative voids. Void 90A extends
through the entirety of substrate structure 94. The depicted
substrate structure 94 includes two outer layers 52, 56 and a
middle layer 54. Fluid channel 32 is formed by forming a void in
middle layer 54. Similarly, an insulative void 90B can be created
by forming a void through middle layer 54. Void 90A which extends
entirely through substrate structure 94 can advantageously be
formed after joining layers 52, 54, 56 to form substrate structure
94. One advantage of forming a void 90B having a height that is the
same as the fluid channel 32 is that it can be formed at the same
time as the fluid channel using the same manufacturing technique
thereby providing manufacturing efficiencies. While void 90A is
open to the ambient atmosphere and will be filled with air, void
90B is enclosed and, if desired, could have a vacuum formed therein
or be filled with a gas other than air. It is also noted that the
insulative void may take on still other forms. For example, it
might be open to the atmosphere at only one end. Alternatively, it
might not conform precisely to the height of middle layer 54. For
example, it could extend partially into layer 52 or not extend the
full extent of middle layer 54. Various other variations on such
insulative voids are also possible.
While the exemplary fluid channel 32 is formed on a fluidic chip,
larger tubes or conduits could alternatively be employed. Various
microfluidic fabrication methods may be employed to manufacture a
fluid channel 32 such as soft lithography, traditional lithography,
laser or plotter cutting, embossing, injection molding,
three-dimensional printing, lamination, extrusion or other suitable
method.
Thermographic image device 46 is positioned to capture an image
that includes at least a portion of downstream section 42.
Advantageously, device 46 is positioned to capture a thermal image
that includes both the downstream section 42 and the upstream
section 44 of fluid channel 32. As discussed above, in the
exemplary embodiment, upstream section 44 of fluid channel 32
upstream of position 40 has a predefined cross section and a
predefined flow path and downstream section 42 of fluid channel 32
downstream of position 40 also has a predefined cross section (FIG.
4) and a predefined flow path (FIG. 2).
The material used to form the outer layer facing thermal imaging
device 46 may advantageously be selected to facilitate the capture
of an image representative of the thermal profile of liquid 24 in
channel 32. For example, the layer may be formed out of a material
substantially transparent or opaque to thermal radiation in the
wavelengths captured in the image. With either approach, it is
advantageous if the thermal information can be conveyed rapidly to
thermal imaging device 46. Another consideration in the choice of
materials is compatibility with the fluid being conveyed. For drug
delivery applications, the biocompatibility of the material will
need to be acceptable.
For example, the outer layer which faces thermal imaging device 46
may be substantially transparent to infrared light such that the
layer acts as a window allowing the thermal imaging device to
capture an image of the fluid medication 24 in channel 32 through
the outer layer. Advantageously, the material is substantially
transparent to radiation having a wavelength of approximately 10
microns. Even more advantageously, the material is substantially
transparent to wavelengths between approximately 1 and
approximately 50 microns. Various materials may be used to form
such a transparent layer such as silicon, polydimethylsiloxane
(PDMS), germanium, zinc selenide, silicon nitride and other
suitable materials which are transmissive for the range of
wavelengths captured by thermal imaging device 46.
Cyclo olefin polymers and copolymers, such as those available under
the tradenames Zeonor and Zeonex, may also be used to form a
substantially transparent layer. In this regard, it is noted that
cyclo olefin polymers and copolymers are not entirely transparent
to infrared light in the typical range of thermal imaging devices,
a sufficiently thin film of such material will be suitably
transparent. Similarly, many materials not typically considered
infrared transparent, will be infrared transparent when formed in a
sufficiently thin film.
Alternatively, the outer layer which faces thermal imaging device
46 may be substantially opaque to infrared light with the thermal
imaging device 46 being positioned to capture an image facing the
opaque layer. Advantageously, the opaque layer would have a
relatively high thermal conductivity whereby it rapidly conducts
heat from the inner (fluid contact) surface of channel 32 to the
outer surface facing thermal imaging device 46. This allows the
exterior surface of the material to quickly assume a temperature
profile representative of the fluid medication 24 in channel 32. It
will also advantageously have relatively high surface emissivity.
These properties will, in turn, allow the thermal imaging device 46
to obtain thermal information about the fluid medication 24 in
channel 32 indirectly. Various materials may be used to form such
an opaque layer such as metals, polymers (which may be thin foils
such as mylar, PLA, silicones, etc.), ceramics, glass, thermally
conductive polymer-ceramic composites and other suitable materials.
Metals, which may be in foil or sheet form, can be advantageous
because of their high thermal conductivity and biocompatibility. If
the selected material does not have a high surface emissivity, a
surface treatment may be applied to increase surface emissivity.
For example, the surface could be painted black.
Some materials may be transparent, or at least partially
transparent, in the range of wavelengths captured by imaging device
46 and also have a high thermal conductivity.
It is additionally noted that, in some applications, one or more
coatings, such as an anti-reflective coating, might be
advantageously employed on the outer layer facing device 46. The
anti-reflective coating may be formed using a silicon-based
material or metal composite. Examples of a suitable material for an
anti-reflective coating include TiSi, SiO.sub.2, TiO.sub.2,
MgF.sub.2, gold, aluminum, ZnSe, ZnS, BaF.sub.2, CaF.sub.2, or
amorphous material transmitting infrared radiation (AMTIR)
anti-reflective chalcogenide glasses. AMTIR anti-reflective
cholcogenide glass is commercially available from Amorphous
Materials, Inc. of Garland. Tex.
Advantageously, the physical size of the fluidic component 32 and
the thermal imaging device 46 of fluid sensing system 30 is
sufficiently small to be conveniently handled by the end user. In
some embodiments, the fluid channel 32 may be mounted on a
substrate having an area of approximately 1 cm.sup.2. Both larger
and smaller sizes, however, may be desirable. For example, some
embodiments might have a fluid channel 32 mounted on a substrate
having sides as small as 0.5 cm each. If infrared microscopy or
special optics are employed, still smaller sizes, wherein the two
sides of the substrate are on the order of tens to hundreds of
microns, might be obtainable. Alternatively, the substrate might
have sides several cm in length or even larger. Other than the
cumbersome nature of larger embodiments, there are very few
constraints on the upper limit of the size of the system.
The image 47 captured by device 46 is communicated to processor 48.
Processor 48 is used to compute at least one output value as a
function of the thermal image wherein that output value is
representative of a parameter of fluid flow through fluid channel
32. Various different parameters can be determined from a
thermographic image. Most directly, the temperature of the fluid
medication 24 can be determined using an image 47. Various other
parameters that can be determined include the volumetric flow rate
of the fluid medication 24 through channel 32, heat capacity of the
fluid, pressure of the fluid; viscosity of the fluid and/or density
of the fluid. The determination of some of these parameters may
require additional information on the system beyond that contained
in the thermographic image 47. Such additional information might
include the dimensions of fluid channel 32.
It is desirable to automate image acquisition and extraction of the
quantities of interest (e.g., flow rate) from the image data. The
task of extracting quantities of interest may be performed by
computer vision algorithms that can identify regions of interest
within a thermal image and track those regions across consecutive
frames. As an example, a heated region and/or a boundary between a
warmer and hotter region may be identified as a "feature". Such a
feature may then be tracked across consecutive frames acquired by
the thermal imager. The rate of motion of such features will
correspond to the rate of flow of the fluid. Computer vision may be
implemented with the use of existing commercial or open-source
computer vision software packages. OpenCV and SimpleCV are examples
of full-featured, open-source computer vision packages that are
appropriate for this application, and which can be implemented on a
variety of computing platforms capable of executing code written in
c, c++, Python, Java, or similar programming languages. An example
of an inexpensive Linux-based computing platform (i.e., processor)
capable of executing computer vision code is the Raspberry Pi.
While OpenCV and SimpleCV computer vision packages offer powerful
image processing capabilities, in certain embodiments it may be
desirable to instead use much simpler image processing algorithms
in order to reduce computing power requirements, and enable
functionality using lower-cost computing platforms (processors).
Examples of some simpler image processing algorithms include
thresholding, locating the brightest and/or dimmest pixels within
an image, and observing changes of intensity in pixels in a time
sequence of images. Since a thermal image may be represented as a
two dimensional array of integers, these simple operations do not
require specialized computer vision algorithms, and can be
performed directly in terms of numerical matrix operations that are
integral to most programming languages. The benefit of using
full-featured computer vision packages is extended functionality,
while the benefit of simpler image processing algorithms is
reduction of cost due to reduced computing power requirements.
As mentioned above, the image data acquired by thermal imaging
device 46 is communicated to processor 48. Processor 48 may be any
suitable processor. One commercially available processor that has
low power requirements and which is well suited for use in fluid
sensing system 30 is the processing module sold by Intel
Corporation under the trademark Edison. Alternatively,
custom-designed ASIC (application-specific integrated circuits) or
custom-designed FPGA (field-programmable gate array) chips could be
used for processor 48.
The output value or values generated by processor 48 is
communicated to display 50 in the exemplary embodiment. The output
value can be utilized for different purposes depending upon the
application. For example, the output value can be communicated to
the user of the delivery device 20. This allows the user (or family
member, caregiver or other medical care provider) to be informed of
the successful delivery of the fluid, e.g., medication, and the
quantity of the delivered fluid, or, that a problem in the delivery
was encountered. Processor 48 may advantageously log any problems
or errors encountered in delivery of the fluid. Successful
deliveries of fluid and the details of such deliveries, such as the
quantity and time of delivery, could also be logged into a memory
module in the processing unit or output to a separate device having
a digital memory for recording such data and/or transmitted by
wireless or wired communication to a medical professional or other
party involved in the care of the patient.
The output value or values generated by processor 48 may also or
alternatively be used to provide active feedback to control
mechanisms such as a fluid pump, valves, thermal device 38, mixing
unit, or other mechanism. Such control feedback can be used to
ensure precise delivery of fluid quantities and that the desired
conditions of fluid delivery are satisfied.
Advantageously, thermal imaging device 46 is aligned and registered
with fluid channel 32 such that each pixel on the sensor of thermal
imaging device 46 corresponds directly to a specific point in the
field of view. Generally, it will be those pixels which correspond
to a specific point in fluid channel 32 can be used to perform
analysis of thermal image 47. In some applications, the thermal
signature of the structure surrounding fluid channel 32 might also
be beneficially employed in the analysis of the thermal image 47.
The input of the known geometry of fluid channel 32 and the
registration of thermal imaging device 46 with fluid channel 32 is
performed before conducting an analysis of acquired images 47.
The temperature of the fluid medication 24 or fluid channel 32 in
direct contact with fluid medication 24 can be measured directly at
each relevant pixel in the thermal image. The velocity of the fluid
flow can be determined in fluid channel 32 in different manners.
For example, by using thermal device 38 in a pulsed mode, a slug of
heated or cooled liquid can be observed flowing through channel 32
to determine the flow velocity. By using thermal device 38 to
provide constant heating or cooling, a steady state temperature
profile can be obtained. For a known fluid, these profiles can be
correlated to a fluid velocity. FIGS. 5-7 illustrate how the
temperature profile of a fluid can vary depending upon the flow
velocity when using the same fluid and same thermal input. In this
regard, it is noted that, for the same fluid and same heat input,
FIG. 5 represents a low flowrate, FIG. 6 represents a medium
flowrate and FIG. 7 represents a high flow rate. With proper
calibration, these profiles can be used to estimate the fluid
velocity. It is noted that, for purposes of graphical simplicity,
FIGS. 5-7 have been simplified and been presented in shades of
black and gray and do not show the full structure and granularity
of an actual thermal image. It is typical, when visually
representing a thermal image for viewing by a human user, to use a
false color representation wherein several different colors and
shades of those colors to more precisely and intuitively represent
the different spot temperatures acquired at each pixel location. It
is noted that when a thermal image will be processed without human
viewing, there is no need to generate a false color image and the
generation of a false color image is done simply to provide a
readily understandable visual image for a human viewer.
In addition to flowrate, it may also be possible to determine the
identity and concentration of the fluid based upon an individual
thermal profile. For example, a library of images of different
known fluids using a known flow rate and a known heat/cooling input
for a given flow channel configuration can be created. Then, a
thermal image can be acquired for the fluid in question when that
fluid is subject to the same flow rate and heat/cooling input for
the same flow channel configuration. The acquired image can then be
compared to the library of images to determine which library image
most closely matches the acquired image. The fluid in question
would then be assumed to have the same characteristics as the fluid
for the matched library image. It is thought that this approach
could be advantageously employed for applications wherein there
would be a limited number of different fluids that might
potentially be used with the fluid sensing system. For example, if
the fluid sensing system is used with a medicament delivery device,
there might be a limited subset of fluids used with the device. In
one such application, the device might be expected to be used only
with fluids which include insulin or human growth hormone at one of
a limited number of predefined concentrations. A thermal image of
each of the predefined concentrations of insulin and of each of the
predefined concentrations of human growth hormone could be included
in the library for comparison with the acquired image.
Characteristics of the fluid can also be obtained by analysis of
one or more acquired images instead of matching the images with
library images. For example, in a pipe or confined channel, the
volumetric flowrate, Q, is defined as the product of fluid velocity
and the cross sectional area of the channel. The dimensions, and
thus cross sectional area of channel 32 are known, thus, once the
fluid velocity within channel 32 is determined, the calculation of
a volumetric flow rate is readily obtained. If the volumetric flow
rate is known and the elapsed time of the flow is also known, the
flow volume, i.e., the volume of fluid which flows past the
monitored point during the elapsed time can be easily determined.
Unless the device includes some feature which diverts part of the
fluid flow, this will also be the volume of fluid which is
discharged through the discharge structure 26. When injecting
medicaments into a patient, the volume of the medicament discharged
through structure 26 will be of significant importance and being
able to precisely monitor the discharged volume is a valuable
feature.
The flow volume can also be more directly determined using sensing
system 30. For example, thermal device 38 can be operated in a
pulsed mode to generate one or more slugs of heated or cooled fluid
at the beginning of the fluid flow. These slugs can then be
monitored to determine how far they travel down the fluid channel.
The dimensions of the fluid channel are known, and thus, the volume
of displaced fluid from the beginning of the fluid flow to the end
of the fluid flow can be readily determined. For example, if a slug
of heated/cooled fluid is generated at the start of an injection
and a thermal image is taken shortly before or at the beginning of
the injection process and at or shortly after the end of the
injection process, the position of the heated/cooled slug of fluid
can be determined at both the beginning and end of the injection
process. The volume of the fluid channel between these two
locations will be the volume of the displaced fluid which will also
be the volume of the fluid discharged through discharge structure
26 absent any diversionary feature. Because the location of the
thermal device 38 is known, it may also be possible to determine
the flow volume with a single thermal image. For example, if the
heated/cooled slug is generated just before initiating the
injection, a single image taken at the end of the injection process
to determine the location of the fluid slug may be sufficient. For
large flow volumes where the initial heated/cooled fluid slug will
be discharged, a series of heated/cooled slugs could be generated
and tracked as they pass through the fluid channel.
Alternatively, if the fluid flow can be controlled sufficiently to
maintain a substantially constant fluid flow, a heated or cooled
slug of fluid could be generated during the course of the fluid
flow. An image could be taken at two separate times, at a known
time interval, to determine the distance the slug of fluid had
traveled during that time period. This would provide a value for
the fluid velocity, which, in turn, could be used to determine the
volumetric flow rate because the cross sectional area of the
channel is known. Once the volumetric flow rate is known, if the
fluid flow is held constant for the entire time the fluid is
discharged and the time period for the fluid discharge is known,
the total volume of fluid discharged could be easily determined. It
may also be possible to use only a single image to determine the
volumetric flow rate if an image is captured at a known time
interval after the creation of the heated/cooled slug of fluid. By
determining how far the slug traveled in a channel of known cross
sectional area during the time period between generation of the
heated/cooled slug and the capture of the image, the volumetric
flow rate can be determined. Once the volumetric flow rate is
determined, the total discharge volume can be determined as
described above.
Spot measurements of the rate of heating/cooling of the fluid by
thermal device 38 can be used to provide a direct measurement of
the specific heat capacity of the liquid flowing in channel 32. In
other words, by taking multiple temperature readings at a selected
pixel location over a known time interval and knowing the amount of
thermal energy supplied or removed by thermal device 38, the heat
capacity of fluid medication 24 can be calculated. Heat capacity is
given by the equation: C=Q/.DELTA.T where C is the heat capacity, Q
is the heat energy provided to (or removed from) the material and
.DELTA.T is the change in temperature. For a resistor-type thermal
device 38, Q may be equated to the energy applied to the resistor,
Q=(V.sup.2/R)*t, where V is the voltage applied to the resistor, R
is the resistance of the resistor and t is duration of the applied
power. By observing the temperature change in fluid medication 24
proximate to location 40 before and after a known voltage is
applied to a resistor of known resistance for a known duration, the
heat capacity of fluid medication 24 can be determined. The thermal
characteristics of flow channel 32 can be calibrated for in advance
using a fluid with a known heat capacity.
Although the heat generated by the resistor can be determined using
the formula set forth above, there generally will be some thermal
loss and not all of the generated heat will be transferred to the
fluid. This heat loss will need to be accounted for when employing
this method. For example, it may be possible to calibrate the
device to account for the heat loss provided that the original
temperature of the fluid and the ambient temperature are within an
intended temperature range.
The determination of the heat capacity of fluid medication 24 can
be particularly useful in applications where it is desirable to
confirm the identity or concentration of a medication being
delivered through channel 32. For example, the heat capacity of a
fluid will typically vary as the concentration of an active
medicine in a liquid carrier (e.g., water) is varied. By measuring
both the total volume delivered and the concentration of the
medication, the correct dosage of a delivered medicine can be
confirmed.
Instead of calculating a heat capacity, a library of images of
different known fluids using a known flow rate and a known
heat/cooling input for a given flow channel configuration could
alternatively be used to identify the fluid and the concentration
of the active ingredient in the fluid as discussed above.
The measured heat capacity and/or use of a library of images might
also be used to monitor the presence or absence of known markers
deliberately added by a drug manufacturer or of contaminants
resulting from counterfeit manufacturing processes that generate
imitation drugs which do not satisfy the manufacturer's original
specifications. Unique thermal features could alternatively or
additionally be added to the reservoir, which may have a seal that
has to be broken when performing the first injection, to confirm
the authenticity of the reservoir and its contents.
The analysis of the thermal images 47 can also be used to identify
obstructions and foreign matter in the fluid flow. Foreign matter,
air bubbles and other obstructions within the fluid flow will have
different thermal characteristics, e.g., heat capacity, and will
generally show up as discrete objects having a different
temperature than the immediately surrounding fluid. Such objects
will generally be easy to identify in the thermal image. In some
applications, the volume of such items can be subtracted from the
total volume delivered to provide a more accurate measurement of
volume of intended fluid that was delivered. The presence of air
bubbles in the fluid might also indicate the presence of a leak. An
appropriate message might be communicated to the user or controller
upon the detection of such bubbles in addition to making
corrections to the determination of flow volume.
Various other parameters can be determined using advanced image
analysis such as fluid viscosity, fluid pressure and fluid density.
In general the motion of an incompressible viscous fluid is
described by the Navier-Stokes equations. These equations can be
solved numerically and their solutions compared to the image data.
It is known to use the Navier-Stokes equations to solve for one or
more of the fluid velocity, pressure and kinematic viscosity when
the boundary conditions for the fluid flow are known. The Reynolds
number (Re) of a liquid can be derived from the Navier-Stokes
equations and is useful for describing when fluid flow is laminar
or turbulent. When using such multi-variable equations to determine
a fluid property, it may be desirable or possibly necessary to
include a second sensor to measure an additional fluid property
such as pressure. An embodiment having such a second sensor is
illustrated in FIG. 8.
Low Reynolds numbers correspond with laminar flow where viscous
forces dominate and fluid flow is smooth with constant motion. High
Reynolds numbers correspond with turbulent flow dominated by
inertial forces and which result in unstable flow patterns. For
flow through a pipe, Re is defined as:
Re=(.rho.vD.sub.H)/.mu.=(vD.sub.H)/v=(QD.sub.H)/(vA) where D.sub.H
is the hydraulic diameter of the pipe, Q is the volumetric
flowrate, A is the pipe cross sectional area, v is the mean
velocity of the fluid, .mu. is the dynamic viscosity, v is the
kinematic viscosity and .rho. is the density of the fluid.
Thermal images acquired by thermal imaging device 46 allow for the
direct visualization of whether the fluid flow is laminar or
turbulent. This provides the possibility of estimating the Reynolds
number based upon the image. In this regard, it is noted that as
the Reynolds number increases the pattern of the turbulence will be
impacted and thereby provides for the possibility of estimating the
Reynolds number based upon the severity of the turbulence. Once the
Reynolds number is known, given a known flow rate, channel geometry
and fluid density, the viscosity can be calculated. Alternatively,
fluid density may be estimated if the viscosity is known. If both
viscosity and fluid density are known, the pressure can be
determined. Similarly, depending on the known variables it can be
possible to calculate the other variables present in the different
Reynolds number relationships.
It is further noted, that fluid density is also related to the
concentration of a dissolved substance in a fluid carrier. For
example, if the identity of the fluid and dissolved substance is
known, once the density of the fluid is determined, the
concentration of the substance in the fluid (e.g., the
concentration of an active ingredient in a medicament) could then
be determined from the density. Alternatively, if the identity and
concentration of the fluid is known, then the density can be
determined.
It is further noted that by configuring fluid channel 32 to have a
number of different sections of varying dimensions such that, for a
given fluid viscosity and flow rate, the onset of turbulence can be
expected in at least one of the sections but not others, the
Reynolds number can be more effectively determined by a simple
visual inspection of the thermal image to determine which sections
of fluid channel 32 have turbulent flow and which do not.
In addition to the detection of turbulent flow, fluid properties
can potentially be determined based on observations of convective
or buoyant flow or diffusion. Viscosity, for example, may be
measured by observing diffusive broadening of a heated flowing band
within a channel under laminar or turbulent conditions. In this
regard, it is noted that by using thermal device 38 in a pulsed
mode, a slug of heated or cooled liquid can be generated and images
showing the sequential broadening and other changes in the shape of
this slug of liquid can be captured with thermal imaging device
46.
Some relevant quantities that are useful to describe convective and
diffusive flow are the Rayleigh number, Ra; the Grashof number, Gr,
and the Prandtl number Pr (the last being an intrinsic property of
a fluid). These, and other, parameters may be estimated from
thermal imaging and define relationships between fluid properties
such as viscosity, diffusivity, thermal conductivity, specific
heat, volume expansion coefficient and fluid density.
When two fluids, or a fluid and a solid, of different temperatures
are mixed together, the thermographic image of the mixing might
also be useful in determining properties of the fluid flow. For
example, a slug of cooled or heated fluid could be generated with
thermal device 38 and its mixing with the surrounding fluid
observed using thermal imaging device 46. Alternatively, a second
fluid line could interject a second fluid at a different
temperature at a point downstream of point 40. In such an
application, the second fluid could potentially be fluid medication
24 which is routed to downstream section 42 through a second
conveyance which does not route the fluid past thermal device 38.
Similarly, a warm fluid could be used to dissolve a cold solid or a
warm fluid could be mixed with cold particles. For example, such
solid particles might be small particles that take the form of a
powder.
It is further noted that when mixing a liquid with particulate
solids to form the fluid that is the subject of the sensor system,
such solids may remain suspended as solids in the liquid or be
dissolved in the liquid to form a solution. As mentioned above with
regard to unwanted air bubbles, the subject fluid might also take
the form of a mixture of liquid and gas whether or not the gas is
intentionally introduced. For example, the purposeful introduction
of a gas could be used to manage the initial temperature of the
fluid.
Another potential use of fluid sensing system 30 is the
verification/authentication of reservoir 22. For example, fluid
sensing system 30 could be used for the authentication of a
disposable medication cartridge containing one or more doses of
medication. This could be accomplished by placing reservoir 22 in
the field of view of thermal imaging device 46 and manufacturing
reservoir 22 to have a characteristic optical, thermal and/or heat
capacity signature that could be verified by the analysis of the
thermal image captured by device 46. This would allow for the
identification and verification of the manufacturer, type of drug,
etc. For instance, a pattern invisible to the naked eye that is
more or less thermally emissive in the range of wavelengths
detected by device 46, or more or less thermally conductive could
be detected in the thermal images captured by device 46. For
example, a metal, ceramic or polymer material could integrated into
a reservoir wall formed out of a different material with differing
thermal properties to form the identifying pattern. Such
identification procedures would be useful for anti-counterfeiting
efforts.
It may also be possible to measure pressure by observing
temperature changes in a sealed reservoir 22 or other vessel in
communication with fluid channel 32 and filled entirely with gas or
both liquid and gas. If the reservoir/vessel was expandable,
expansion of the reservoir/vessel could be used to determine
pressure. Alternatively, changes in gas pressure could result in
observable temperature changes potentially observable using thermal
imaging device 46.
It is also possible to utilize a second fluid sensor in combination
with thermal imaging device 46. While temperature and flow rate,
flow volumes readily obtained using thermal imaging device 46,
obtaining accurate measurements of viscosity and density using only
a thermal imaging device 46 presents greater difficulties as
discussed above. As a result, such additional values might not be
obtainable or have the desired accuracy when using only a thermal
imaging device 46. Utilizing a second fluid sensor to measure a
property of the fluid provides two measurements which can be used
in known fluid formulas to more reliably and accurately determine
fluid properties such as viscosity, density and fluid identity.
FIG. 8 schematically depicts an example of such a system employing
an additional sensor 66. Sensor 66 is advantageously a miniaturized
sensor such as a micro electro-mechanical system (MEMS) fluid
pressure sensor. Such small scale fluid pressure sensors are
commercially available and typically provide a sensor and signal
conditioning electronics on a single chip thereby providing a small
scale fluid sensor. Sensor 66 is coupled with controller 48 whereby
the sensed fluid pressure can be communicated to controller 48. As
discussed above, by obtaining both a sensed fluid pressure and one
or more thermographic images, the determination of fluid properties
is enhanced. The system 20A depicted in FIG. 8 is the same as that
shown in FIG. 1 except for the addition of sensor 66. Although a
pressure sensor is shown in the embodiment of FIG. 8A, other types
of sensors could also be used depending upon the type of
application for which the device will be employed.
Depending upon the particular application, it may only be necessary
to obtain a single pressure measurement at the same time as the
capture of a thermographic image. In other applications, it may be
desirable to continuously monitor the pressure. In the illustrated
embodiment, the location of the pressure sensor is shown upstream
of inlet 34. In alternative embodiments, however, sensor 66 could
be coupled with channel 32 proximate thermal device 38 or elsewhere
on channel 32 or between outlet 36 and the discharge structure 26.
In other words, the sensor may be operably coupled with the fluid
medication being transferred from the reservoir to the discharge
structure at any point between the reservoir and discharge
structure provided that the arrangement allows for obtaining the
desired measurement. Depending on the type of sensor, it may either
directly or indirectly obtain the desired measurement.
For example, FIG. 8A depicts a MEMS pressure sensor 66 coupled with
a side chamber 74 that is in fluid communication with main fluid
channel 32 in the downstream section 42 of channel 32. Such a side
chamber is suitable for use with some types of sensors under
certain conditions, however, it may not be suitable for all sensors
or under all flow conditions.
FIG. 9 depicts a medical delivery device 20B which utilizes a
reusable electronics package 68 while much if not all of the
remainder of the system is disposable. Electronics package 68
includes the thermal imaging device 46 and controller 48. It would
also include the display 50 if a display is to be used with the
device. Housing 70 may be either reusable or disposable. If a
simple and inexpensive arrangement, such as a manual plunger 72, is
used for the driving mechanism, it may be advantageous for housing
70 and plunger 72 to be disposable. If a more elaborate driving
mechanism, such as a battery powered motor, is used, it will
generally be desirable for the housing and driving mechanism to be
reusable.
If a disposable housing 70 is used, electronics package 68 is
detachably secured to housing 70 using a snap fit, threaded
engagement or other suitable arrangement. If the housing is
intended to be reused, electronic package 68 may be permanently
secured to the housing.
The reservoir 22 used in the embodiment of FIG. 9 includes a
cylindrical barrel 76 and a piston 78. The advancement of piston 78
by the driving mechanism expels the fluid medication through the
opposite end of barrel 76 and into the fluid channel 32. Fluid
channel 32 may be formed on a chip that is mounted on an exterior
surface of reservoir 22 as schematically depicted in FIG. 9. Fluid
channel 32 might also be mounted directly on the exterior of
reservoir 22. Both the reservoir 22 and fluid channel 32 may be
disposable. The discharge structure 26 may take the form of a
hollow needle adapted to inject a fluid into a living organism.
Advantageously, discharge structure 26 is disengageable from the
medication delivery device and is thereby disposable after a single
use.
Cooperating Luer fittings on the fluid channel 32 and the needle
assembly 26 allow the needle assembly to detached after a single
use and replaced with a new needle assembly. The use of Luer
fittings to attach injection needles to syringes and allow for the
separate disposal of a used needle are well known to those having
ordinary skill in the art. This arrangement allows for the use of a
new needle for each injection from a reservoir 22 that contained
more than one dosage when originally filled. It is additionally
noted that the fluid medication 24 used with the illustrated
embodiments is a liquid medication.
As mentioned above, both reservoir 22 and fluid channel 32 may be
disposable. In this regard it is noted that an electrical resistor
mounted on fluid channel 32 would also generally be discarded with
the reservoir and fluid channel 32 if an electrical resistor was
used as the thermal device 38. In such an embodiment, the surface
or substrate on which channel 32 and the electrical resistor was
mounted could have exposed electrical contacts that would be
abutted into electrical communication with similar contacts on
electronic package 68 or on housing 70. For example, if a
non-electrically powered drive mechanism was used, the contacts
could be located on electronic package 68 which would generally
include a battery for powering the electronics mounted therein and
this battery could also be used for supplying electrical current to
the electrical resistor acting as a thermal device. If, instead, a
battery powered motor was installed in housing 70 and used as the
drive mechanism, electrical contacts could be mounted in housing 70
to couple the electrical resistor with the batteries powering the
drive mechanism 28.
Once the contents of reservoir 22 are depleted, the disposable
components of the system are discarded. For some embodiments, this
may include both the reservoir 22 and fluid channel 32. For other
embodiments, it might also include housing 70 and drive mechanism
28. For example, if the drive mechanism were a polymeric manually
operable plunger 72, it may be cost effective to dispose of the
plunger at the same time as the reservoir 22.
The embodiment 20B includes a fluid channel 32 supported on
reservoir 22. Alternative arrangements, however, are also possible.
For example, fluid channel 32 could be supported on the needle
assembly. For applications, however, where the needle assembly will
be discarded after each use and the reservoir holds more than one
dosage, mounting the fluid channel 32 on the needle assembly will
generally not be the most desirable. It is also possible for the
fluid channel 32 arrangement to be separable from both the
reservoir 22 and the discharge structure 26. This arrangement may,
however, require the use of mating Luer fittings at both the
reservoir 22 to fluid channel 32 interface and at the fluid channel
32 to discharge structure 26 interface. By permanently mounting the
fluid channel 32 on reservoir 22, only the fluid channel 32 to
discharge structure 26 interface would require Luer fittings to
allow for the separate disposal of the discharge structure 26 after
each use.
While several of the components of the fluid sensing system can be
cost-effectively formed as disposable components, it will generally
be desirable for the electronics package 68 to be re-usable. By
designing the electronics package to be non-destructively separable
from the disposable components of the system, the electronics
package can be conveniently re-used after detachment and disposal
of the disposable components. Generally, this will mean that the
thermal imaging device 46 and processor 48 are non-destructively
separable from the reservoir 22 and fluid channel 32. If the system
includes a display 50, it will generally be part of the re-usable
electronics package and also be non-destructively separable from
the disposable components. As mentioned above, some of the other
components may be either disposable or re-usable. For example, the
housing 70 and driving mechanism may be either re-usable or
disposable. If such components are disposable, it will be
advantageous for the electronics package 68 to be non-destructively
separable from the housing and driving mechanism. If these
components are re-usable, it may still be desirable to have the
electronics package 68 be non-destructively separable from these
components so that if the driving mechanism fails, it would not be
necessary to replace the electronics package when replacing the
driving mechanism.
FIG. 10 is generally similar to embodiment of FIG. 9 but uses a
different fluid channel. In this embodiment 20C, the fluid channel
is wrapped around columnar barrel 76 of reservoir 22 to form a
helical coil 82. In this embodiment, barrel 76 has a cylindrical
shape, however, other columnar barrels having an elongate shape,
for example, an elongate reservoir having a rectangular cross
section, could also be used. Helical coil 82 is formed out of a
thin walled tube which is either heat conductive or generally
transparent to the radiation in the wavelengths captured by the
thermal imaging device 46. Helical coil 82 can be secured in place
with adhesive or by other suitable means.
A length of tubing 84 extends rearwards from the distal end of
reservoir 22 where the reservoir discharges into the tubing. The
tubing is then wrapped around the barrel 76 of reservoir 22
progressing in the distal direction. Proximate the distal end of
reservoir 22, the tubing has a fitting for engagement with a
cooperating fitting on the injection needle assembly forming
discharge structure 26. In the illustrated embodiment, the fittings
are Luer fittings. Similar to the embodiment 20B of FIG. 9,
reservoir 22 and fluid channel 32 of embodiment 20C can be
disposable with needle assembly 26 also being separately
disposable.
A significant fraction of the fluid channel 32 that forms helical
coil 82 is hidden from view of the thermal imaging device 46 by
barrel 76 of reservoir 22. Those portions of helical coil 82 which
are in the line-of-sight of thermal imaging device 46 form discrete
segments of fluid channel 32. In other words, thermal imaging
device 46 is positioned to capture discrete discontinuous portions
of the downstream section of fluid channel 32. Thermal device 38
can be positioned such that all of the discrete portions of fluid
channel 32 captured by thermal imaging device 46 are downstream of
thermal device 38, or, it may be positioned so that thermal imaging
device 46 captures discrete portions of fluid channel 32 both
upstream and downstream of thermal device 38. Similarly, thermal
device 38 may be positioned to be in the field of view of thermal
imaging device 46 or hidden from view.
One advantage provided by the use of fluid channel formed into a
helical coil 84 is that the distance from the inlet to the outlet
of the fluid channel 32 is greater than if the entirety of the
fluid channel 32 was in the field of view of the camera. When
forming only a single heated slug of fluid, this arrangement
provides a greater length of fluid channel 32 for the slug to
travel through before exiting the field of view of thermal imaging
device 46 in comparison to a serpentine or spiral shaped fluid
channel.
It is noted that while the end point of the fluid slug that will be
used to determine the final length of travel for the slug in such
an embodiment may be hidden from view by the barrel 76 of reservoir
22, with proper calibration, the overall thermal profile of the
fluid should allow for the determination of the final position of
the slug even when it is hidden from view behind reservoir 22.
FIG. 11 illustrates an embodiment 20D that is similar to 20C but
wherein a projection 86 has been formed on barrel 76 of reservoir
22 to hold that portion of the fluid channel 32 which is in the
field of view of thermal imaging device 46 in a substantially
planar configuration to thereby simplify the analysis of the
thermal images.
The reservoir in this embodiment still has a columnar shape and
fluid channel 32 which is wrapped about that portion of the
reservoir having projection 86 extending therefrom a defines a
helical coil. Although the shape of reservoir 22 is not perfectly
cylindrical and fluid channel 32 conforms to the planar surface 87
defined by projection 86, fluid channel 32 is still wrapped about a
columnar structure and advances axially along the columnar
structure with each winding about the columnar structure and, thus,
is helical for purposes of the present application.
Also visible in FIG. 11 is a feature 88 with unique thermal
signature such as a uniquely shaped metal component embedded in a
polymeric material forming projection 86. Advantageously, feature
88 is positioned on reservoir 22 such that it falls within the
field of view of thermal imaging device 46 when reservoir 22 is
installed in housing 70. Alternatively, a void or some other
thermally identifiable feature in reservoir could provide the
unique thermal signature. As mentioned above, the use of such an
item with a unique thermal signature embedded in reservoir 22 can
be used to authenticate and/or identify reservoir 22 and its
contents.
While this invention has been described as having an exemplary
design, the present invention may be further modified within the
spirit and scope of this disclosure. This application is therefore
intended to cover any variations, uses, or adaptations of the
invention using its general principles.
* * * * *